Practice question

**Axial versus equatorial** field comparison shows B_axial = 2 B_eq for same r. Using μ₀ = 4π×10⁻⁷ T·m/A, calculation involves r³ = (0.3)³ = 0.027 m³, so B = 10⁻⁷·m/r³ yields moment estimation. B = (μ₀/4π) (m/r³) , so m = (B r³/(μ₀/4π)) . Given: B = 5 × 10⁻⁶ T , r = 0.4 m , (μ₀/4π) = 10⁻⁷ . m = (5 × 10⁻⁶ × (0.4)³/10⁻⁷) = (5 × 10⁻⁶ × 0.064/10⁻⁷) = 3.2 A m² . Substituting values gives 3.2 A m², which matches expected magnitude for this magnetic configuration, confirming dipole field dependence on m/r³ and torque relation τ = m B sinθ.